1. Field of the Invention
The invention pertains to stabilized thermoplastic molding compositions on the basis of polyvinyl chloride or essentially vinyl chloride-containing polymers.
2. Statement of the Related Art
In the molding processing of thermoplastic polymers to form pipes, bottles, shapes, films and the like, for example by extrusion, injection molding, blowing, deep drawing and calandering, degradation of the plastic can easily take place at the high temperatures thus occurring. This leads to undesirable discolorations and impairment of the mechanical properties. For this reason stabilizers are added to the polymers prior to thermal deformation to oppose such degradation. For polyvinyl chloride and essentially vinyl chloride-containing mixed polymers, the principal thermal stabilizers used are inorganic and organic lead salts, organic antimony compounds, organotin compounds, and cadmium/barium carboxylates and phenolates. The metal compounds mentioned are usually designated as primary stabilizers; secondary stabilizers or costabilizers are often added to improve their efficacy. Further details on the thermal stabilizers customarily employed for vinyl chloride polymers can be taken from the relevant literature, for example the Encyclopedia of Polymer Science and Technology, Vol. 12, New York, London, Sydney, Toronto, 1970, pp. 737 to 768.
The stabilizers mentioned show a fully satisfactory effect in practice. However, certain objections exist to the use of lead, antimony and cadmium compounds, especially toxicologic objections.
A number of organotin compounds are toxicologically unobjectionable, but their broad use is impeded by their high price. For this reason attempts have long been made to replace these compounds by less objectionable and more advantageously priced substances. For this reason it has become customary to use as primary stabilizers fatty acid salts, aromatic carboxylates and phenolates of the metals calcium, barium, zinc and aluminum, perhaps supplemented by costabilizers such as organic phosphites, imino compounds, epoxy compounds, polyhydric alcohols or 1,3-diketones. However, these new stabilizer systems involve to a greater or lesser degree the defect that they give an inadequate initial stability and/or inadequate long-term stability to the molding compositions to be stabilized. Therefore a need exists for substances with the aid of which the initial and/or long-term effect of such stabilizer systems can be decisively improved.